Ethylene and propylene, light olefin hydrocarbons with two or three atoms per molecule, respectively, are important chemicals for use in the production of other useful materials, such as polyethylene and polypropylene. Polyethylene and polypropylene are two of the most common plastics found in use today and have a wide variety of uses for both as a material fabrication and as a material for packaging. Other uses for ethylene and propylene include the production of vinyl chloride, ethylene oxide, ethylbenzene and alcohol. Steam cracking or pyrolysis of hydrocarbons produces essentially all of the ethylene and propylene. While hydrocarbons used as feedstock for light olefin production include natural gas, petroleum liquids, and carbonaceous materials including coal, recycled plastics or any organic material, an important source is naphtha where larger paraffins and naphthenes are cracked to produce olefins.
One means of increasing propylene yields from a naphtha cracker is to add a metathesis reactor. A metathesis reactor can convert a portion of a feedstream comprising ethylene and butene to propylene. However, the metathesis reaction uses some of the ethylene which otherwise would be used as a product, and the butene stream needs to have isobutenes removed, as well as having 1-butene removed to improve the performance of the metathesis reactor.
As the demand for propylene increases, it is highly desirable to be able to shift production of propylene without having to create a new type of reactor, or to replace expensive existing equipment.